Interesting, CKAN was considering Firespitter, Firespitter Core and Firespitter Resources config as "required" before the last patch. With the patch only the core modul is considered "required" and therefore the firespitter mod can be absent while using ProbePlus!.
Not sure why this was, but I assumed your modification was responsible for this change.
Still: thanks for your work, KSP gains so much due to the modding community!